1. Field of the Invention
The present invention relates to medical guide wire in which a characteristic of mechanical strength is improved at a welded portion between a thin core wire and a helical spring body welded together by means of welding member.
2. Description of Related Art
As a general usage, a distal end of a medical guide wire, i.e., a welded portion between a core wire and a helical spring body requires a specified mechanical strength to insure a safety measure. For this purpose, various types of medical guide wires have been introduced.
In Japanese patent application publication No. 4-25024, a helical spring body has a radiopaque portion and a radiotransparent portion, both of which are placed around a core wire, and screwed at a brazed section between the radiopaque portion and the radiotransparent portion.
This method makes it possible to weld not only helical spring bodies of different types of material but helical spring bodies of stainless steel metal. The stainless steel metal is used to visually recongnize in fluoroscopy. The brazing procedure is used to simply weld the helical spring bodies.
In Japanese patent application publication No. 10-513081, to a distal end portion of a core wire, a helical spring body is secured which has a radiopaque coil portion and a radiotransparent coil portion. The coil portions are welded by means of a laser spot welding, brazing or soldering procedure. So are the coil portions welded to the core wire.
The method makes it possible to weld the core wire to the helical spring body even when either the core wire or the helical spring body is made of the stainless steel metal. By welding both the distal ends of the helical spring body to the respect ends of the core wire, it becomes possible to prevent the helical spring body from being acutely bent at the welded end portions while permitting a helical spring body to move freely at a portion between the welded end sections. The brazing procedure, however, is used to simply weld the helical spring body to the core wire as identified in the above case.
In Japanese Laid-open patent application publication No. 2006-297152, a helical spring body is disclosed which comprises a plurality of thickened wires and secured to a core wire by means of a brazing or soldering procedure. This enables an operator to equally bend the helical spring body at the welded portions. As mentioned in the previous cases, the brazing procedure is also used to simply weld the helical spring body to the core wire.
In the prior art medical guide wires, the brazing procedure functions simply as a welding means upon welding the helical spring body to the core wire (stainless steel wire). No eutectic alloy has been used as a welding member when implementing a brazing or soldering procedure on a core wire. No core wire has been made by drawing a stainless steel wire while considering a thermal influence on the mechanical strength of the core wire.
Therefore, the present invention has been made with the above drawbacks in mind, it is a main object of the invention to provide a medical guide wire which enables an operator to use in safety by improving a tensile strength of the core wire and a welding strength by making use of advantageous effect of the tensile strength due to the thermal influence on the core wire without using the welding member simply as a securement means when the austenitic stainless steel is used to the core wire and is drawn as a wrought-out procedure.